Conditional Compilation example- try catch statement

In the beginning of the tutorial, I mentioned how conditional compilation got
a boast to its profile when it started showing up in some Ajax related
JavaScripts. I'll show you what I mean here. A Ajax script usually contains a
central function for testing support for the objects needed to make asynchronous
requests in IE and Firefox:

Most people think the "try/catch" statements will gracefully test for Ajax
support, though unfortunately that's not true. Browsers that do not support
"throw/catch", such as IE4.x, will in fact choke on the above code and return an
error. To overcome this, conditional compilation can be used to create a truly
cross browser friendly Ajax processing function:

Using conditional compilation, the entire try/catch block is only rendered by
IE5+, sparing browsers like IE4 or non IE browsers from trying to dicipher it.
Firefox obviously will pick up on and use XMLHttpRequest instead. And there you
have it- a truly cross browser ajax function!